1. Field of the Invention
The present invention relates to a process and an apparatus for molding a 3-D (three-dimensional) molded product from a sheet. More specifically, it relates to a technology for controlling the thickness of the 3-D molded product.
2. Description of Related Art
A skin 100 of an instrument panel, as shown in FIG. 20, is molded by heating and softening a thermo-plastic resin sheet while clamping its peripheral part, by pressing the sheet into a vacuum-mold by a plug so as it to be deformed while elongated, and by adhering the sheet to a 3-D molding surface by vacuuming and suctioning it by the vacuum-mold. A crimp pattern (not shown), which is formed on the 3-D molding surface, is transferred to the surface of the instrument panel skin 100.
Because the sheet is deformed while elongated as described above, the thickness of the skin 100 is thinned in comparison to the thickness of the original sheet. However, as shown in FIG. 21, problematically, the color, feel, strength, and other attributes of a convex top part 101 (the region where the sheet is molded in vacuum by being pressed into a deep concave part of the 3-D molding surface) and its side part 102 of the skin 100 differ from the other parts because the elongation percentage is very large and the skin is very thin there.
Then, in order to suppress the elongation percentage of the convex top part 101 and the side part 102 to assure a certain thickness, the following measures have been taken solely or in combination:
(1) Contrive the shape of the plug;
(2) Adjust a gap between the 3-D molding surface and the plug;
(3) Adjust the slipperiness of the sheet by pasting a tape, cloth, sandpaper and the like on the plug;
(4) Cool the sheet partially by the plug; and
(5) Partially adjust the heating temperature of the sheet.
However, the thickness of the convex top part 101 and the side part 102 has not been assured by the measures described above. Also, it has been impossible to improve the thickness to a value equal to or more than a thickness obtained by multiplying the inverse of a multiplying factor of the surface area of the mold (multiplying factor of the surface area of the 3-D molding surface to an area of a flat sheet on which the 3-D molding surface is projected) by the thickness of the original sheet.
It is an object of the present invention to provide a process and an apparatus for molding a 3-D molded product, which allow the thickness of the 3-D molded product formed from a sheet or the thickness of a convex top and side parts to be assured.
The process of the present invention involves molding a 3-D molded product from a sheet. The molded product includes a product section, which turns out to be a product, and an extra product section, which is to be excised. The sheet is made of a thermoplastic polymeric material. The process comprises the steps of clamping the sheet at its peripheral edge; heating and softening the sheet; deforming the heated and softened sheet by stretching the sheet along a 3-D molding surface of a mold; and adhering the sheet to the 3-D molding surface to mold the 3-D molded product. A thickness of the product section is made up by moving the sheet material at the extra product section to the product section during the deforming step by partially releasing (loosing) a tensile stress of the extra product section.
The method for partially releasing the tensile stress of the extra product section is not specifically limited and the following modes (1) and (2) may be adopted, for example.
(1) A cutting section, such as a cut, a hole, or a cutout is created on a sheet region, which turns out to be the extra product section, before or during the deformation. As shown in FIGS. 19A-19J, the shape of the cutting section (51) is not specifically limited. The cut may be a straight line or a curve, the hole may be a circle, an oval, or an oblong shape and the cutout may be V-shaped or U-shaped, as shown in FIGS. 19A-19J, in order from the top. Circular holes may be created at the edges of the cut, as shown in FIG. 19I. Or the cutting section may be intermittent, as shown in FIG. 19J. The cutting section from which a sharp edge is removed like the circular, elliptical and U-shape cutting sections and ones in which circular holes are created at the ends of the cut prevent the sheet from breaking unnecessarily at the edge. The cutting section may be created manually or by a cutting mechanism.
(2) A peripheral edge of a sheet region, which turns out to be the extra product section, has not been clamped before or during the deformation.
Although the mold is not specifically limited, a vacuum-mold and a compressed air-mold may be adopted, for example. When a vacuum-mold is used, it is preferable that the sheet is suctioned from a part of the 3-D molding surface corresponding to the product section so as the sheet to be adhered to the part, and that the sheet is not suctioned from a part of the 3-D molding surface corresponding to a sheet missing part, which is created after moving the sheet material at the extra product section during the adhering step.
Preferably, the sheet is deformed while being elongated along the 3-D molding surface by being pressed into the mold by a plug. Preferably, the plug is formed such that a gap between the plug and the 3-D molding surface after the sheet is pressed ranges from a value approximately equal to a thickness of the sheet after being pressed, which is thinner than that before being pressed, to a value 3 mm greater than a thickness of the sheet before being pressed. However, it is possible for the gap to be larger than that range at exceptional regions, such as the vertical region and the undercut region.
Another aspect of the present invention is an apparatus for molding a 3-D molded product from a sheet. The molded product includes a product section, which turns out to be a product, and an extra product section, which is to be excised. The sheet is made of a thermoplastic polymeric material. The apparatus comprises a clamp mechanism for clamping the sheet at its peripheral edge; a mold having a concave 3-D molding surface; and a plug for deforming the sheet while elongating the sheet along the 3-D molding surface by pressing the sheet into the mold. The mold or the plug is provided with a cutting mechanism for creating a cutting section at a sheet region, which turns out to be the extra product section, before or during the deformation.
Still another aspect of the present invention is an apparatus for molding a 3-D molded product from a sheet. The molded product includes a product section, which turns out to be a product, and an extra product section, which is to be excised. The sheet is made of a thermoplastic polymeric material. The apparatus comprises a clamp mechanism for clamping the sheet at its peripheral edge; a mold having a concave 3-D molding surface; and a plug for deforming the sheet while elongating the sheet along the 3-D molding surface by pressing the sheet into the mold. The clamp mechanism is arranged so that a peripheral edge of a sheet region, which turns out to be said extra product section, has not been clamped before or during the deformation.
When the mold is a vacuum-mold in the above respective apparatus, it is preferable that the vacuum suction pores are created at a part of the 3-D molding surface corresponding to the product section and that no vacuum suction pores are created at a part of the 3-D molding surface corresponding to a sheet missing part, which is created after moving the sheet material at the extra product section.
In the same manner, when the mold is a vacuum-mold, it is preferable that the mold or the plug is provided with a sealing member for preventing a vacuum leak from a sheet missing part, which is created after moving the sheet material at the extra product section. The sealing member may be a plate-like, bar-like, or ring-like sealing member made of heat resistant rubber foam or resin foam.
The vacuum-mold is not specifically limited and the following molds (a) to (f) are examples.
(a) A mold manufactured by a process which comprises electro-forming a main body of the mold on the surface of a mandrel having an electrically conductive layer having a plurality of very small, non-conductive portions on its surface so that very small, undeposited portions may be formed on the non-conductive portions at the beginning of the electro-forming operation, and may grow with the progress of the operation to eventually form a plurality of pores through the wall of the main body of the mold, as disclosed in Japanese Patent Publication No. 2-14434.
(b) A mold manufactured by a process which comprises electro-forming a main body of the mold on the surface of a mandrel having an electrically conductive layer having no very small, non-conductive portions on its surface in an electro-forming solution containing less than a substantial amount of the surface active agent so that very small, undeposited portions may be formed on the surface of the electrically conductive layer at the beginning of the electro-forming operation, and may grow with the progress of the operation to eventually form pores through the wall of the main body of the mold, as disclosed in Japanese Patent Publication No. 5-39698.
(c) A mold manufactured by a process which comprises electro-forming an electro-formed shell on the electrically conductive surface of a mandrel having very small pores of a diameter of 30 to 1000 xcexcm on its electrically conductive surface in an electro-forming solution containing less than a substantial amount of the surface active agent so that undeposited portions may be formed on the openings of the very small pores in the beginning of the electro-forming operation, and may grow with the progress of the operation to eventually form pores through the wall of the electro-formed shell, as disclosed in Japanese Patent Laid-Open Specification No. 5-156486.
(d) A mold manufactured by a process comprising the steps of preparing a mandrel having an electrically conductive surface; forming a poreless first electro-formed layer on the conductive surface in an electro-forming solution containing a substantial amount of a surface active agent to form the front side of a shell; removing the mandrel and the layer from the solution; forming through the layer, small straight pores, each having an approximately equal diameter along a length thereof; and forming a second electro-formed layer on a back side of the first layer in an electro-forming solution containing less than a substantial amount of a surface active agent to form a back side of the shell, while undeposited hollow portions are formed in alignment with the straight pores in initial formation of the second layer, the hollow portions enlarging to form diametrically enlarged pores through the second layer, the enlarged pores having a diameter, which becomes larger toward a surface of the second layer opposite from the first layer, as disclosed in U.S. Pat. No. 5,728,284.
(e) A permeable porous mold manufactured by flame-coating melted metal drops.
(f) A mold manufactured by creating pores on the mold which has had no permeability by means of mechanical work (drill or the like), laser works and others.
Although the material of the thermoplastic polymeric material for the sheet is not specifically limited, the following materials may be used, for example:
(i) Thermoplastic synthetic resin, including polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, saturated polyether, polyamide, vinyl acetate copolymer, and the like, for example.
(ii) Thermoplastic elastomer (TPE) including polyolefine (TPO), polyurethane (TPU), and stylene elastomers, for example.
Further objects of this invention will become evident upon an understanding of the illustrative embodiments described below. Various advantages not specifically referred to herein but within the scope of the instant invention will occur to one skilled in the art upon practice of the presently disclosed invention. The following examples and embodiments are illustrative and not seen to limit the scope of the invention.